1. Field of the Invention
The present invention relates to a method and apparatus for recording information on an information recording medium such as a magnetooptical disk and, more particularly, to an information recording method and apparatus, which serve to perform so-called direct verification for confirming recorded information simultaneously with recording.
2. Related Background Art
As a recording method for a magnetooptical recording apparatus, an optical modulation method, a magnetic field modulation method, and the like are known. The magnetic field modulation method is superior to other methods since it can directly overwrite new data on old data. FIG. 1 is a schematic view showing an arrangement of a magnetooptical recording apparatus adopting the magnetic field modulation method. In a magnetooptical disk 1 as an information recording medium, a magnetooptical recording layer 3 is formed on a transparent substrate 2, and a protective layer 4 is formed on the upper surface of the recording layer 3. The magnetooptical disk 1 is rotated at a constant speed by driving a spindle motor 5. Furthermore, a magnetic head 6 is arranged above the upper surface of the magnetooptical disk 1, and an optical head 7 is arranged below the lower surface of the disk 1 so as to oppose the magnetic head 6.
When information is recorded on the magnetooptical disk 1 by the magnetooptlcal recording apparatus, a laser beam emitted from the optical head 7 is radiated on the magnetic recording layer 3 to form a beam spot having a spot size of about 1 .mu.m, while the disk 1 is rotated at high speed. Upon radiation of the laser beam, the temperature of the recording layer 3 is increased to be higher than the Curie temperature of the layer. At the same time, the magnetic head 6 applies, onto the heated portion, a bias magnetic field modulated according to recording information by driving a drive circuit 8. Thus, the direction of magnetization of the heated portion of the magnetooptical recording layer 3 is oriented in the direction of the bias magnetic field. Upon movement of the beam spot, as the heated portion is cooled, the direction of the magnetization on the recording layer 3 is fixed, and information is recorded as a pit.
When the above-mentioned information recording is performed, information cannot often be normally recorded due to defects, deterioration, or corrosion of the magnetooptical disk 1, dust attached onto the disk 1, or the malfunction of the apparatus. For this reason, verification is normally performed. In this verification, recorded information is reproduced as a magnetooptlcal signal by the optical head after one revolution of the disk from the recording of the information, and the recording signal and the reproduction signal are compared to check if they are identical with each other. The reason why the verification is performed after one revolution of the disk is that a recording laser beam is normally used common to a reproduction laser beam, and it is difficult to reproduce recorded information simultaneously with recording or immediately after recording. However, the above-mentioned verification requires a time for two revolutions of the disk, i.e., a time required for recording information for one track (one revolution of the disk), and a time required for checking recorded information. Thus, the signal processing time is prolonged, and the recording speed is lowered.
In order to solve this problem, a magnetooptical recording method for reproducing a recording information signal from reflected light of a recording beam simultaneously with information recording, and checking if the recorded signal is identical with the signal to be recorded, is proposed in Japanese Laid-Open Patent Application No. 3-73448. Furthermore, the present applicant filed a further improved magnetooptical recording method of the above-mentioned method in U.S.S.N. 913,481 (filed on Jul. 14, '92). According to this magnetooptical recording method, since recording of an information signal and checking of recorded information can be simultaneously performed, the time required for checking the recorded information becomes unnecessary, and the information recording speed can be remarkably increased.
However, the above-mentioned magnetooptical recording method allows verification simultaneously with recording, i.e., one-beam direct verification using a single light source. In this case, a signal reproduced simultaneously with recording undesirably includes an old information component left on an information track. Therefore, if the number of old information components included in the reproduced signal is increased, the reliability of the verification signal is deteriorated due to crosstalk of the old information components. For this reason, it is demanded to further improve the reliability of verification.